Method and arrangement for the classification of objects occupying a seat

ABSTRACT

A method and a system in the classification of objects occupying a seat, in particular for the reliable control of the triggering of restraint systems in motor vehicles. Utilized are the dynamics of a person seated on the seat, based on the acceleration forces acting on the person. Using the variables of these forces and the force exerted on the seat cushion of the seat by the mass of the person and its change, there is a determination, as a redundant variable, the mass, the location of the center mass and other physical variables and these are used for the reliable classification.

FIELD OF THE INVENTION

The present invention relates to a method and a system in theclassification of objects occupying a seat, in particular for theclassification-dependent triggering of restraint systems in motorvehicles.

BACKGROUND INFORMATION

To protect the occupants of a motor vehicle in accidents, seats of themotor vehicles have been provided not only with reversible restraintarrangements such as safety belts, but also with irreversible restraintarrangement such as airbags, which are triggered, for examplepyrotechnically fired, when a collision is detected.

However, faulty firing or firing at the wrong time, even if an accidenthas occurred, may result in serious injuries that would not occur if theairbag were not fired or, in the case of multistage airbags, were firedin some other way. Furthermore, unnecessary firing must be avoided,especially when the seat is not occupied or is occupied only by anobject and not a person.

U.S. Pat. No. 5,570,903 discusses systems for detecting child seats bysensors arranged in the seat surface, for example, or to detect theoccupation state, as in U.S. Pat. No. 5,983,147, by video monitoring,for instance. However, this is still not sufficient. Instead, to avoiddisadvantageous and sometimes even dangerous triggering in particularsituations, it must be ascertained whether a person occupying the seatis tall or short, heavy or light, is close to the instrument panel or isleaning back in the seat. Depending on the individual situation, therestraint arrangement must be triggered in a variety of ways once anaccident occurs, which applies in particular to an airbag able to befired in several stages, again especially in the case of an airbag for afront-seat passenger. A division into groups, i.e., a classification,has shown to be sufficient.

For this purpose, the so-called OC system (occupant classificationsystem) has been developed. This system is based on an empiricallydetermined correlation between the body weight and the spacing of theischiadic tubers of a person. As a result, a pressure profile may beacquired and analyzed with the aid of pressure sensors, which arearranged in a matrix-like manner in a seat. This analysis, first of all,also allows or provides for detecting whether or not the seat isoccupied. Furthermore, a distinction may be made whether a child seat orsome other object or a person is in an occupied seat.

If a person has been detected as object, a further classification maytake place by a corresponding analysis of the pressure profile on thebasis of empirical findings that correspond to the body size and thebody weight of the seated person. Furthermore, using suitable sensors,the absolute weight of the object in the seat may be detected. Forexample, the weight of the seat with the object may be measured with theaid of foil strain gauges, for instance. On the other hand, the pressuredifferential between an occupied and an unoccupied seat using a sensorsuch as a pressure foil, installed in the seat itself, may be detected,thereby detecting the absolute weight of the object.

The conventional classification utilizes empirical findings, which inindividual cases, which are of interest here, may provide wrong resultsin the control of the triggering of the restraint arrangement, however.

SUMMARY OF THE INVENTION

Using this point of departure, it is thus an object of the exemplaryembodiment and/or exemplary method of the present invention to improvethe accuracy of a classification.

Furthermore, it is an object of the exemplary embodiment and/orexemplary method of the present invention to provide a system forcarrying out or performing a corresponding method.

The exemplary embodiment and/or exemplary method of the presentinvention, first of all, is based on the finding that higher redundancyof the ascertained variable results in the desired improvement.Furthermore, the exemplary embodiment and/or exemplary method of thepresent invention builds on the finding that, due to the dynamics of amotor vehicle, an object in the examined seat is also exposed to forcesacting on the object in a dynamic manner. Furthermore, these dynamicforces are measurable, that is, ascertainable as to their magnitude. Onthe basis of known physical laws, knowledge of these forces and the typeof positional change of the object caused by these forces allow veryaccurate conclusions to be drawn regarding physical variables of theobject, in particular a person seated in the seat, such as mass, heightof the center mass (over the seat), height/width ratio of this centermass.

These variables increase the redundancy in the determination of relevantvariables on the basis of which the control of the trigger means isimplemented when an accident has occurred. In particular thediscrimination and, as the case may be, the classification of the personoccupying a seat, is improved with respect to the variables that areimportant for the control of the trigger means. To this end,conventional and possibly already installed passenger compartmentsystems may be used to determine the (additional) variables that arerelevant in this context, so that no or only a few new additionalsensors are required. Such detection systems in the passengercompartment are video monitoring, detection of the absolute weights bymeans of foil strain gauges, ultrasound detection, radar systems, an OCgrid mat and the like.

German patent application no. 100 51 312.3 (filed in Germany on Oct. 17,2000), and assigned to Bosch GmbH) discusses a system and method fordetecting the dynamics of a pressure profile exerted on the seat by aseated person and to derive therefrom a dynamic factor that indicateswhether the object or the person is stationary or moving. Thisinformation allows an evaluation whether the dynamic factor originateswith a rigid object or a person because they have different dynamiccharacteristics, in this way allowing this information to be consideredin the decision whether or not a trigger means should be triggered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of a system for implementing themeasures of the exemplary embodiment and/or exemplary method of thepresent invention.

FIG. 2 shows a schematic block diagram of the function of the measuresof the exemplary embodiment and/or exemplary method of the presentinvention.

DETAILED DESCRIPTION

FIG. 1 shows a seat 4 made up of a seat cushion 1, a backrest 2 and ahead restraint 3, the seat being located in a schematically shown motorvehicle 5. Furthermore, FIG. 1 shows as an object a person 6 seated inseat 4 and schematically shows center mass 7 of this person 6. In amanner known per se, seat 4 is assigned restraint systems so as toprotect person 6 in the event of an accident or some other dangeroussituation. Irreversibly triggerable restraint systems 8, such asairbags, pyrotechnically ignitable seat-belt tighteners and the like,are schematically illustrated by a block. These restraint systems 8 aretriggered or fired via a triggering device 9 as soon as a dangeroussituation for person 6 must be assumed on the basis of recorded andascertained criteria.

As is generally known per se and will not be discussed in more detail,it is initially ascertained whether seat 4 or its seat cushion 1 isoccupied in the first place, for no triggering of restraint systems 8via control device 9 will be considered when seat 4 is not occupied.

Furthermore, it is essential that restraint systems 8 be triggered onlywhen a person 6 is in seat 4, but not when an object, such as a childseat, is occupying seat 4. The discrimination between a person 6occupying seat 4 and an object occupying seat 4 may be realized, forexample and in particular, in that the pressure distribution exerted onseat cushion 1—the pressure profile—is recorded, which is schematicallyillustrated in FIG. 1 by a pressure sensor 10. A person 6 acts on seatcushion 1 and thus pressure sensor 10 via two spaced ischiadic tubers,whereas objects, also child seats, act on pressure sensor 10 by a verydifferent pressure profile.

Such a pressure profile is able to be ascertained by at least two, orthree or four individually spaced pressure sensors in seat 4 or seatcushion 1. A matrix arrangement of pressure sensors in the sense of aso-called OC mat is particularly advantageous.

Incidentally, signal D or a group of signals corresponding to such apressure profile also allows to ascertain the occupation state of seat 4as such in a conventional manner and also to determine the mass actingon seat 4 or seat cushion 1, for example according to vertical forcecomponent z acting at center mass 7 of the (non-moving) person 6.

For example, from the spacing of the ischiadic tubers, which may beascertained by means of pressure sensor 10, and this weight component,i.e., z-component, it is already possible on the basis of empirical datato draw conclusions as to the size of person 6 or the height of centermass 7 of person 6, that is to say, a classification is able to beimplemented.

This means that signal D allows a trigger circuit 11 to utilize signalscorresponding to the mass of person 6 and/or center mass 7 of person 6for the calculation of control signals for trigger device 9, eitheralone or also together with other signals. In the latter case, theredundancy is already improved.

According to the exemplary embodiment and/or exemplary method of thepresent invention, a very precise determination of the position ofcenter mass 7 of person 6 is possible when the acceleration of person 6,and thus in particular its center mass 7, is detected at leastqualitatively in a horizontal plane. In the event of an impact againstan obstacle, person 6, and thus its center mass 7, is subjected to adynamic movement represented by an arrow 12. This movement may beconsidered unbraked in the horizontal plane and thus be equated with theacceleration of vehicle 5 determined with the aid of vehicle-sidesensors.

That is to say, using at least two acceleration sensors in a horizontalplane in vehicle 5 (not individually shown), it is possible to determinethe dynamic movement, i.e., the acceleration movement, of person 6 orits center mass 7 in a horizontal plane. This is schematicallyillustrated in FIG. 1 by an x-component and a y-component.

In FIG. 1, this is also shown schematically in that a computing circuit13 receives external signals such as from corresponding accelerationsensors and utilizes these to calculate the x- and y-components,evaluates them and transmits them to trigger circuit 11. A dashed lineindicates that such sensors may possibly ascertain the z-component aswell (in addition). As mentioned, this z-component may also beascertained on the basis of signal D.

The dynamics of person 6 represented by arrow 12 thus determine the typeof position change of person 6 in response to externally acting forces.If these forces are known in their magnitude as well, the actuallypresent position of person 6 and its center mass 7 may be determinedextremely precisely (cf., for example, Gillespie, T. D., Fundamentals ofVehicle Dynamics, Society of Automotive Engineers Inc., Warendale,U.S.A., 1992, and/or Kuypers, F., Klassische Mechanik (ClassicMechanics), 3rd edition, VHC Verlagsgesellschaft mbH, Weinheim, 1990).These may then be utilized, in the sense of a detection that is improvedvia redundancy, in the classification for the purpose of triggeringrestraint systems 8.

Together with other variables, in any event, the mass, height of centermass 7, and also the height/width ratio of center mass 7, essentiallyeven redundantly, (width in this case representing a measure for the inparticular lateral displacement of the center mass in a tiltingmovement), may be determined, and then used for a classification so asto achieve the most optimal triggering of restraint system 8, especiallyan airbag, with the aid of control device 9 as a function of theindividual dangerous situation.

The afore-discussed functional principle is shown again in FIG. 2.

Since the signals required for the mentioned utilization of the dynamicsof person 6 are normally already ascertained in the vehicle, additionalsensors are also no longer required.

1-9. (canceled)
 10. A method for classifying an object occupying a seat,for a classification-dependent triggering of a restraint system in amotor vehicle, the method comprising: determining first forces acting onthe object in a horizontal plane as to their magnitude, and secondforces exerted on the seat by the object in a direction that is verticalwith respect to the horizontal plane as to their magnitude; anddetermining at least a change over time of the forces acting on theobject and at least physical variables of the object, the determiningbeing done by calculating, from variables of the forces and a type oftheir change over time, and using these for the classifying.
 11. Themethod of claim 10, further comprising: determining at least one of aposition of a center mass of the object, a mass, a weight and a heightof the center mass of the object, a height/width ratio of the centermass of the object, from the determined forces.
 12. The method of claim10, wherein the physical variables and other characteristic quantitiesof the object are used for the classifying.
 13. The method of claim 10,wherein external forces acting on the object are dynamic forces.
 14. Themethod of claim 10, wherein, based on the forces acting on the seat inthe vertical direction and their distribution in the seat, adiscrimination is determined as between an object and a person as theobject, and wherein the classifying is implemented only if the personhas been discriminated as being the object.
 15. The method of claim 14,wherein a pressure profile acting on one of the seat and a seat cushionis determined, recorded, and used for the discriminating.
 16. A systemfor classifying an object occupying a seat, for aclassification-dependent triggering of a restraint system in a motorvehicle having acceleration sensors in the vehicle for detecting dynamicforces acting on the object, comprising: a first determining arrangementto determine first forces acting on the object in a horizontal plane asto their magnitude, and second forces exerted on the seat by the objectin a direction that is vertical with respect to the horizontal plane asto their magnitude; and a second determining arrangement to determine atleast a change over time of the forces acting on the object and at leastphysical variables of the object, the determining being done bycalculating, from variables of the forces and a type of their changeover time, and using these for the classifying.
 17. The system of claim16, wherein there are at least two sensors, arranged in the seat withclearance, for the determining of the pressure profile of the object.18. The system of claim 17, wherein there are at least three sensors.19. The system of claim 17, wherein there are at least four sensors. 20.The system of claim 17, wherein there is a matrix arrangement of sixsensors.